K3 output buffer modification

[K2QI]

Hello group,

Just finished installing the K3 output buffer modification this afternoon.
I used the SMD resistor, and not the leaded part.  Anyway, the most
difficult aspect was soldering the replacement back on and ensuring it
didn't move.  I think I was successful.  I may have chipped a tiny piece of
the black surface of the resistor off with the tip of the screwdriver used
to hold it in place during soldering.  I believe its fine as I still get a
13k ohm reading from my multimeter.  I know I shouldn't test with the
resistor already soldered, but its the best I can do for now.

Anyway, question here is how do I test to make sure that the mod was
successful?  Unfortunately I do not have a spectrum analyzer.  Better yet,
how to ensure that my modification didn't screw anything up?  Anything I
should test for right away?

Mni tnx es vy 73,
James K2QI
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[Alan Bloom-2]

If you have a second receiver, you could connect it to the K3 IF output.
Tune the second receiver to 8.215 MHz and you should hear whatever the
K3 is hearing at a similar signal level.  (About an S-unit lower with
the K3 preamp off, one S-unit higher with preamp on.)

Alan N1AL


On Wed, 2010-01-06 at 14:20 -0500, James Sarte wrote:

> Hello group,
>
> Just finished installing the K3 output buffer modification this afternoon.
> I used the SMD resistor, and not the leaded part.  Anyway, the most
> difficult aspect was soldering the replacement back on and ensuring it
> didn't move.  I think I was successful.  I may have chipped a tiny piece of
> the black surface of the resistor off with the tip of the screwdriver used
> to hold it in place during soldering.  I believe its fine as I still get a
> 13k ohm reading from my multimeter.  I know I shouldn't test with the
> resistor already soldered, but its the best I can do for now.
>
> Anyway, question here is how do I test to make sure that the mod was
> successful?  Unfortunately I do not have a spectrum analyzer.  Better yet,
> how to ensure that my modification didn't screw anything up?  Anything I
> should test for right away?
>
> Mni tnx es vy 73,
> James K2QI
> ______________________________________________________________
> Elecraft mailing list
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[K2QI]

Hi Alan,

Unfortunately, I do not have a second receiver.  Is there a way I can test
output voltages with my meter - anything at all to just confirm that the
resistor is indeed working?

Anyway, the rig passed the smoke test upon turning on so that's a good start
right there.

James K2QI

On Wed, Jan 6, 2010 at 3:26 PM, Alan Bloom <[hidden email]> wrote:

> If you have a second receiver, you could connect it to the K3 IF output.
> Tune the second receiver to 8.215 MHz and you should hear whatever the
> K3 is hearing at a similar signal level.  (About an S-unit lower with
> the K3 preamp off, one S-unit higher with preamp on.)
>
> Alan N1AL
>
>
--
73 de James K2QI
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[Alan Bloom-2]

Unfortunately you won't be able to measure an RF signal at the IF output
connector with a meter or oscilloscope unless you have a REALLY strong
signal at the K3 antenna input.

As a general sanity check, you could do a DC voltage measurement on the
JFET just to make sure it is still drawing current.  I don't know the
exact voltage, but I imagine you should get a volt or two on the JFET
source (R9 source resistor).  That does require taking the bottom panel
off the K3 again.

Alan N1AL


On Wed, 2010-01-06 at 15:33 -0500, James Sarte wrote:

> Hi Alan,
>
> Unfortunately, I do not have a second receiver.  Is there a way I can
> test output voltages with my meter - anything at all to just confirm
> that the resistor is indeed working?
>
> Anyway, the rig passed the smoke test upon turning on so that's a good
> start right there.
>
> James K2QI
>
> On Wed, Jan 6, 2010 at 3:26 PM, Alan Bloom <[hidden email]> wrote:
>         If you have a second receiver, you could connect it to the K3
>         IF output.
>         Tune the second receiver to 8.215 MHz and you should hear
>         whatever the
>         K3 is hearing at a similar signal level.  (About an S-unit
>         lower with
>         the K3 preamp off, one S-unit higher with preamp on.)
>        
>         Alan N1AL
>        
>        
>        
>
> --
> 73 de James K2QI

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[K2QI]

Hmm... just out of curiosity, couldn't I measure the IF output using the XG2
signal generator set to 50uV?  How strong does the signal have to be?

I'll go ahead and check the junction voltage at R9 as you suggested.

Mni tnx!
James K2QI


-----Original Message-----
From: Alan Bloom [mailto:[hidden email]]
Sent: Wednesday, January 06, 2010 4:44 PM
To: James Sarte
Cc: Elecraft
Subject: Re: [Elecraft] K3 output buffer modification

Unfortunately you won't be able to measure an RF signal at the IF output
connector with a meter or oscilloscope unless you have a REALLY strong
signal at the K3 antenna input.

As a general sanity check, you could do a DC voltage measurement on the
JFET just to make sure it is still drawing current.  I don't know the
exact voltage, but I imagine you should get a volt or two on the JFET
source (R9 source resistor).  That does require taking the bottom panel
off the K3 again.

Alan N1AL


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[Don Wilhelm-4]

James,

What do you propose to measure a 50 uV signal with?  If you have
equipment that will measure levels that low, then well and good, but if
you are expecting to see it on an oscilloscope or RF Probe, you may as
well forget it.  Recall that 50 uV is an S-9 level, and is -73 dBm which
is a very low level to measure.

There are power measurement devices that will detect levels that low,
but most of the commercial ones are priced out of the range of
amateurs.  One that can be homebrewed and will measure levels down to
-80 dBm is the W7ZOI  design using the AD8307 Logarithmic Amplifier as
the front end (see Experimental Methods in RF Design, Measurements
chapter or the QST article from June 2001 p38ff).  To calibrate it, one
must have a known level source of RF at two different levels.  Those
with a calibrated HP8640 signal generator (or similar) will be able to
calibrate that meter with no problem.
For anyone considering building such an instrument, understand that it
must be well shielded.  Stray coupling into the meter will produce
erroneous results.  Mine is in a shielded enclosure with an internal
battery, and even that is not enough, the front end circuits are
shielded from the rest of the assembly.  Yes, it can even measure the
total signal level coming in from an antenna, so it is a good performer
if properly calibrated and is a very sensitive detector.  With the 40 dB
Power Tap, it can accurately measure power levels up to +50 dBm (100
watts), and will work up to 500 MHz with careful construction.  If you
want accurate power measurements, consider building one, but you need
access to a calibrated power source to calibrate it - calibrate at 10
MHz, 50 MHz, 144 MHz and 450 MHz so you have a good idea of the
variation with frequency - there will be some variation.

73,
Don W3FPR

James Sarte wrote:
> Hmm... just out of curiosity, couldn't I measure the IF output using the XG2
> signal generator set to 50uV?  How strong does the signal have to be?
>
> I'll go ahead and check the junction voltage at R9 as you suggested.
>
> Mni tnx!
> James K2QI
>  
>
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[K2QI]

Hi Don,

I don't have anything that sensitive, so that's out.  Perhaps I can borrow a
spectrum analyzer from someone near me... or just wait for the P3 to come
out.  That's the only reason I performed the mod in the first place.

BTW, thanks for the QST article info... will give that a read tonight.  

Cheers!
James K2QI

-----Original Message-----
From: Don Wilhelm [mailto:[hidden email]]
Sent: Wednesday, January 06, 2010 6:37 PM
To: James Sarte
Cc: 'Elecraft'
Subject: Re: [Elecraft] K3 output buffer modification

James,

What do you propose to measure a 50 uV signal with?  If you have
equipment that will measure levels that low, then well and good, but if
you are expecting to see it on an oscilloscope or RF Probe, you may as
well forget it.  Recall that 50 uV is an S-9 level, and is -73 dBm which
is a very low level to measure.

There are power measurement devices that will detect levels that low,
but most of the commercial ones are priced out of the range of
amateurs.  One that can be homebrewed and will measure levels down to
-80 dBm is the W7ZOI  design using the AD8307 Logarithmic Amplifier as
the front end (see Experimental Methods in RF Design, Measurements
chapter or the QST article from June 2001 p38ff).  To calibrate it, one
must have a known level source of RF at two different levels.  Those
with a calibrated HP8640 signal generator (or similar) will be able to
calibrate that meter with no problem.
For anyone considering building such an instrument, understand that it
must be well shielded.  Stray coupling into the meter will produce
erroneous results.  Mine is in a shielded enclosure with an internal
battery, and even that is not enough, the front end circuits are
shielded from the rest of the assembly.  Yes, it can even measure the
total signal level coming in from an antenna, so it is a good performer
if properly calibrated and is a very sensitive detector.  With the 40 dB
Power Tap, it can accurately measure power levels up to +50 dBm (100
watts), and will work up to 500 MHz with careful construction.  If you
want accurate power measurements, consider building one, but you need
access to a calibrated power source to calibrate it - calibrate at 10
MHz, 50 MHz, 144 MHz and 450 MHz so you have a good idea of the
variation with frequency - there will be some variation.

73,
Don W3FPR

James Sarte wrote:
> Hmm... just out of curiosity, couldn't I measure the IF output using the
XG2
> signal generator set to 50uV?  How strong does the signal have to be?
>
> I'll go ahead and check the junction voltage at R9 as you suggested.
>
> Mni tnx!
> James K2QI
>  
>

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[Terry Schieler]

Did something change or am I misunderstanding Jim's post here.  I thought
that the IF Output Buffer Mod would not be necessary with the P3.  If one
does the IF buffer mod for the LP Pan now, how is the P3 affected in the
future?  Does it then need to be reversed?

73,
Terry, W0FM

-----Original Message-----
From: James Sarte [mailto:[hidden email]]
Sent: Wednesday, January 06, 2010 5:59 PM
To: [hidden email]
Cc: 'Elecraft'
Subject: Re: [Elecraft] K3 output buffer modification

Hi Don,

I don't have anything that sensitive, so that's out.  Perhaps I can borrow a
spectrum analyzer from someone near me... or just wait for the P3 to come
out.  That's the only reason I performed the mod in the first place.

BTW, thanks for the QST article info... will give that a read tonight.  

Cheers!
James K2QI



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[John Seney]

GreAt question!

73

John WD1V

Sent from my iPhone


On Jan 7, 2010, at 11:16 AM, "Terry Schieler" <[hidden email]
 > wrote:

> Did something change or am I misunderstanding Jim's post here.  I  
> thought
> that the IF Output Buffer Mod would not be necessary with the P3.  
> If one
> does the IF buffer mod for the LP Pan now, how is the P3 affected in  
> the
> future?  Does it then need to be reversed?
>
> 73,
> Terry, W0FM
>
> -----Original Message-----
> From: James Sarte [mailto:[hidden email]]
> Sent: Wednesday, January 06, 2010 5:59 PM
> To: [hidden email]
> Cc: 'Elecraft'
> Subject: Re: [Elecraft] K3 output buffer modification
>
> Hi Don,
>
> I don't have anything that sensitive, so that's out.  Perhaps I can  
> borrow a
> spectrum analyzer from someone near me... or just wait for the P3 to  
> come
> out.  That's the only reason I performed the mod in the first place.
>
> BTW, thanks for the QST article info... will give that a read tonight.
>
> Cheers!
> James K2QI
>
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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>
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[srife]

        Apparently not, because this mod is included on all new K3s


Stan Rife
W5EWA



-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of John Seney
Sent: Thursday, January 07, 2010 10:22 AM
To: Terry Schieler
Cc: Elecraft; <[hidden email]>
Subject: Re: [Elecraft] K3 output buffer modification

GreAt question!

73

John WD1V

Sent from my iPhone


On Jan 7, 2010, at 11:16 AM, "Terry Schieler"
<[hidden email]
 > wrote:

> Did something change or am I misunderstanding Jim's post here.  I  
> thought
> that the IF Output Buffer Mod would not be necessary with the P3.  
> If one
> does the IF buffer mod for the LP Pan now, how is the P3 affected in  
> the
> future?  Does it then need to be reversed?
>
> 73,
> Terry, W0FM
>
> -----Original Message-----
> From: James Sarte [mailto:[hidden email]]
> Sent: Wednesday, January 06, 2010 5:59 PM
> To: [hidden email]
> Cc: 'Elecraft'
> Subject: Re: [Elecraft] K3 output buffer modification
>
> Hi Don,
>
> I don't have anything that sensitive, so that's out.  Perhaps I can  
> borrow a
> spectrum analyzer from someone near me... or just wait for the P3 to  
> come
> out.  That's the only reason I performed the mod in the first place.
>
> BTW, thanks for the QST article info... will give that a read tonight.
>
> Cheers!
> James K2QI
>
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
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[Bill W4ZV]

Terry Schieler wrote

Did something change or am I misunderstanding Jim's post here.  I thought
that the IF Output Buffer Mod would not be necessary with the P3.  If one
does the IF buffer mod for the LP Pan now, how is the P3 affected in the
future?  Does it then need to be reversed?

An unmodified K3's IF OUT has 7-17 dB transfer loss that cannot be compensated for in ANY panadaptor, so the mod is necessary for the P3.

http://cliftonlaboratories.com/elecraft_k3_and_panadapters.htm#What_then_is_the_transfer_gain_of_the_K3_

73,  Bill

[K2QI]

Terry, where did you see that the buffer mod wouldn't be necessary for the
P3?  The P3 is the only reason why I performed this modification!  Hopefully
someone can clarify this...

73 de James K2QI

-----Original Message-----
From: Terry Schieler [mailto:[hidden email]]
Sent: Thursday, January 07, 2010 11:17 AM
To: 'James Sarte'; [hidden email]
Cc: 'Elecraft'
Subject: RE: [Elecraft] K3 output buffer modification

Did something change or am I misunderstanding Jim's post here.  I thought
that the IF Output Buffer Mod would not be necessary with the P3.  If one
does the IF buffer mod for the LP Pan now, how is the P3 affected in the
future?  Does it then need to be reversed?

73,
Terry, W0FM


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[Bill W4ZV]

Bill W4ZV wrote

An unmodified K3's IF OUT has 7-17 dB transfer loss that cannot be compensated for in ANY panadaptor, so the mod is necessary for the P3.

http://cliftonlaboratories.com/elecraft_k3_and_panadapters.htm#What_then_is_the_transfer_gain_of_the_K3_

Jack Smith's comment on the page above "Telepostinc's LP-PAN has a built-in amplifier to overcome the transfer gain problem." is incorrect.  LP-PAN **DOES** require the mod and N8LP posted a mod similar to Elecraft's back in July 2008.  

http://groups.yahoo.com/group/LP-PAN/files/K3_Buffer_Mod/

73,  Bill

[Eric Swartz - WA6HHQ]

This resistor value change has been in effect on all new K3s shipped
since September of 2009.

See:
http://www.elecraft.com/K3/k3_app_notes.htm

It will definitely improve the MDS of anything hooked to the IF port,
including the P3.

73, Eric
----



James Sarte wrote:

> Terry, where did you see that the buffer mod wouldn't be necessary for the
> P3?  The P3 is the only reason why I performed this modification!  Hopefully
> someone can clarify this...
>
> 73 de James K2QI
>
> -----Original Message-----
> From: Terry Schieler [mailto:[hidden email]]
> Sent: Thursday, January 07, 2010 11:17 AM
> To: 'James Sarte'; [hidden email]
> Cc: 'Elecraft'
> Subject: RE: [Elecraft] K3 output buffer modification
>
> Did something change or am I misunderstanding Jim's post here.  I thought
> that the IF Output Buffer Mod would not be necessary with the P3.  If one
> does the IF buffer mod for the LP Pan now, how is the P3 affected in the
> future?  Does it then need to be reversed?
>
> 73,
> Terry, W0FM
>  

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[Iain MacDonnell - N6ML-2]

On Thu, Jan 7, 2010 at 9:32 AM, Bill W4ZV <[hidden email]> wrote:

>
>
>
> Bill W4ZV wrote:
>>
>> An unmodified K3's IF OUT has 7-17 dB transfer loss that cannot be
>> compensated for in ANY panadaptor, so the mod is necessary for the P3.
>>
>> http://cliftonlaboratories.com/elecraft_k3_and_panadapters.htm#What_then_is_the_transfer_gain_of_the_K3_
>>
>
> Jack Smith's comment on the page above "Telepostinc's LP-PAN has a built-in
> amplifier to overcome the transfer gain problem." is incorrect.  LP-PAN
> **DOES** require the mod and N8LP posted a mod similar to Elecraft's back in
> July 2008.
>
> http://groups.yahoo.com/group/LP-PAN/files/K3_Buffer_Mod/

Sorry, but it's NOT *required*. It may be strongly recommended, but
it's not required. I've been using LP-Pan successfully for months
without the mod. I'm sure it's not optimal. and once in a while there
are signals that I can copy by ear through the K3 that CW Skimmer
can't decode, but to say that the mod is *required* is a bit of an
overstatement.

Quoting from N8LP's website:

"K3 Buffer Mod Simple mod that improves noise floor of panadapter
display by reducing loss in the K3 IF output. Not required, but some
users have found it well worth the effort. The link takes you the
Files section of the LP-PAN User Group. Elecraft now offers a mod kit
very similar to ours, and has incorportated the mod into current
production K3s."

    ~Iain / N6ML
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[Bill W4ZV]

Iain MacDonnell - N6ML-2 wrote

Sorry, but it's NOT *required*. It may be strongly recommended, but
it's not required. I've been using LP-Pan successfully for months
without the mod. I'm sure it's not optimal. and once in a while there
are signals that I can copy by ear through the K3 that CW Skimmer
can't decode, but to say that the mod is *required* is a bit of an
overstatement.

Perhaps not if you're happy to give away 17 dB of sensitivity.  My primary use of LP-PAN is for a waterfall to detect weak signals on 160.  It was obvious when I first got LP-PAN working in April 2008 that there was a major sensitivity problem.

http://n2.nabble.com/K3-Buffer-Mod-tt741709.html#a741709
http://lists.contesting.com/archives//html/CQ-Contest/2008-05/msg00357.html

73,  Bill

[Jack Smith-6]

The LP-Pan has an AD 8007 input amplifier, the same amplifier I use in
the Z10000 buffer amp.

In the LP-Pan, the AD8007's gain is set by a combination of fixed
resistors and a potentiometer. Quickly working through the numbers,
varying the potentiometer from one end to the other results in gain
ranging from +6 dB to +15 dB, net of the 6 dB loss in the series 49.9
ohm resistor. (Measured at the AD8007's output pin, the  gain is 6 dB
above these values, but in order to drive a capacitive load, a series
49.9 ohm resistor is added between the output pin and the load. This
results in 6 dB loss if the load is 50 ohms.)

The main reason one might wish to apply the buffer modification to the
K3 instead of cranking up the LP-Pan gain or purchasing one of my Z10000
buffer amplifiers is that a somewhat improved noise figure will result
if the K3's IF output follower loss is reduced. In practice, the
improvement in noise figure is not huge as the overall NF is set mostly
by the early gain stages in the K3.

Jack K8ZOA




On 1/7/2010 12:32 PM, Bill W4ZV wrote:

>
>
> Bill W4ZV wrote:
>    
>> An unmodified K3's IF OUT has 7-17 dB transfer loss that cannot be
>> compensated for in ANY panadaptor, so the mod is necessary for the P3.
>>
>> http://cliftonlaboratories.com/elecraft_k3_and_panadapters.htm#What_then_is_the_transfer_gain_of_the_K3_
>>
>>      
> Jack Smith's comment on the page above "Telepostinc's LP-PAN has a built-in
> amplifier to overcome the transfer gain problem." is incorrect.  LP-PAN
> **DOES** require the mod and N8LP posted a mod similar to Elecraft's back in
> July 2008.
>
> http://groups.yahoo.com/group/LP-PAN/files/K3_Buffer_Mod/
>
> 73,  Bill
>    

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[Bill W4ZV]

Jack Smith-6 wrote

The main reason one might wish to apply the buffer modification to the
K3 instead of cranking up the LP-Pan gain or purchasing one of my Z10000
buffer amplifiers is that a somewhat improved noise figure will result
if the K3's IF output follower loss is reduced. In practice, the
improvement in noise figure is not huge as the overall NF is set mostly
by the early gain stages in the K3.

Another reason to reduce transfer loss inside the K3 is that you're not forced to use the internal PREamplifier to compensate for the loss at IF OUT.  If you enable PRE to get more output to LP-PAN, you potentially risk degrading the dynamic range of the K3 itself by applying more gain than needed to its internal IF chain.

73,  Bill

[N8LP]

Because of the gain distribution, when the K3 preamp is on the improvement in overall noise figure due to the buffer mod is less obvious than when the preamp is off. The preamp dominates the noise figure when it's on, but the buffer loss dominates the noise figure when the preamp is off. Since it's generally smart to run with the preamp off on the lower bands, therefore, the mod is quite helpful for low band use.  

Larry N8LP

Bill W4ZV wrote

Jack Smith-6 wrote

The main reason one might wish to apply the buffer modification to the
K3 instead of cranking up the LP-Pan gain or purchasing one of my Z10000
buffer amplifiers is that a somewhat improved noise figure will result
if the K3's IF output follower loss is reduced. In practice, the
improvement in noise figure is not huge as the overall NF is set mostly
by the early gain stages in the K3.

Another reason to reduce transfer loss inside the K3 is that you're not forced to use the internal PREamplifier to compensate for the loss at IF OUT.  If you enable PRE to get more output to LP-PAN, you potentially risk degrading the dynamic range of the K3 itself by applying more gain than needed to its internal IF chain.

73,  Bill